This invention relates to a method and apparatus for detecting and separating foreign objects that may become mixed in a single-flowing stream of particulate matter being transported on a conveying system. More particularly, the present invention relates to a system for detecting latex material buried in a stream of tobacco leaf product and removing the latex pieces prior to further processing of the tobacco flow. Even more particularly, the present invention relates to a means for detecting latex in a stream of tobacco utilizing a multi-spectral, infrared camera detection system.
Tobacco as delivered for processing into cigarettes may contain undesired foreign material therein. In the early stages of handling the tobacco, particularly in the fields during harvesting and storing, laborers may wear latex gloves and, from time to time, the gloves can come off or pieces of them can get mixed in with the tobacco. Once the contaminated tobacco reaches the processing lines at the manufacturing plants, the pieces of latex may be buried deep in multiple layers of tobacco leaves, said multiple layers often being up to 14-16 leaves deep. In the past, it was necessary to station laborers along conveyor lines to inspect the incoming tobacco and manually remove the foreign material, but because to the naked eye the appearance of latex so resembles the color and shape of tobacco, this manual process has been largely ineffective and tends to substantially slow process and production flow rates.
A system is taught in U.S. Pat. No. 4,657,144 (Marin) which scans the surface of cut tobacco as it flows on a conveyor belt to detect pieces of white paper that may get into the tobacco from the ripping machines used to recycle defective cigarettes. The surface of the tobacco flow is brightly illuminated and the white papers which is far more reflective than tobacco, is detected by measuring spikes in reflectance levels. Air nozzles are then activated to deflect portions of the tobacco containing paper as the tobacco falls from one conveyor line to another.
Marin references another system wherein the surface of cut tobacco as it moves on a conveyor line is scanned by a camera sensitive to certain colors of visible light. An integrated color mapping of the scanned tobacco is compared to the desired color, and the off-color tobacco is rejected using an air nozzle system similar to the one described above.
In both systems referenced above, only the surface of the tobacco is scanned as the material passes beneath an optical sensing device, therefore only foreign material which happens to be on the surface of tobacco bed will be detected and subsequently rejected.
To attempt to circumvent the limitation of mere surface detection, a variation of Marin, as taught in U.S. Pat. No. 4,657,144, scans cut tobacco as it cascades from one conveying system to another, illuminating the tobacco as it falls and detecting reflected light from pieces of paper. When paper pieces are detected, air nozzles provide a fluid blast of air to deflect the contaminated portion of tobacco.
The shortcoming of the prior art is that none detect foreign material having similar color, shape and density as tobacco, such as latex. Further, merely scanning the surface of a tobacco flow does not detect foreign material when it is buried below the surface or layered within leaves. Nor does the prior art overcome the problem that latex has a very similar visual appearance to tobacco, especially when tobacco dust has coated the latex, making it even more difficult to detect by eye or reflective light technology. Thus, a means of scanning through layers of a moving substance to detect foreign material buried therein is desired.
One method in the prior art U.S. Pat. No. 3,004,664 (Dreyfus) teaches determining the presence and concentration of a particular substance in a stationary mixture of substances by means of comparing the intensities of radiations passed through the mixture at a plurality of wave lengths, without requiring a standard reference for each spectral determination. An egg bloodspot detector is taught whereby light is transmitted through an egg, after which the light is split into two beams and each beam, after passing though an aperture for weighting, is filtered for a certain bandwidth and focused onto a photocell. The photocell produces electrical signals which are compared by a voltage detector coupled with an amplitude discriminator, and passed to an activator means.
However, the prior art does not overcome problems encountered when the substance is in motion, nor when the material has varying depths and layers, nor when the material displays problematic diffractions, such as are encountered in certain particulate matter, such as tobacco leaf edges.